CN110646272B - Method for purifying hydrophilic ionic liquid - Google Patents
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- C07D233/00—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings
- C07D233/54—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members
- C07D233/56—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring carbon atoms
- C07D233/58—Heterocyclic compounds containing 1,3-diazole or hydrogenated 1,3-diazole rings, not condensed with other rings having two double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring carbon atoms with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, attached to ring nitrogen atoms
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/3103—Atomic absorption analysis
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/3103—Atomic absorption analysis
- G01N2021/3114—Multi-element AAS arrangements
Abstract
The invention provides a purification method of hydrophilic ionic liquid, which comprises the following steps: contacting sodium sulfide with a first alkaline medium, dissolving in ultrapure water, filtering, adding hydrophilic ionic liquid into the filtrate, contacting with a second alkaline medium, standing for precipitation, and filtering to obtain a liquid containing the first product. The invention can effectively remove heavy metal ions in the ionic liquid by using a sodium hydroxide rolling sweeping sulfide precipitation method.
Description
Technical Field
The invention relates to the field of heavy metal ion detection and analysis, in particular to a purification method of hydrophilic ionic liquid.
Background
Ionic liquids are organic liquid substances that consist entirely of ions at or near room temperature, and generally consist of larger organic cations and smaller inorganic anions. The ionic liquid as a green solvent is widely applied to the fields of chemical separation, organic synthesis, electrochemistry, material processing and the like, and can be mainly used as a raw material for preparing a catalyst, a novel biological adsorbent, a flame retardant and the like. In addition, the ionic liquid has unique and excellent properties, such as good thermal stability and chemical stability, nonflammability, wide liquid range, strong dissolving capacity, good conductivity, wide electrochemical window, low vapor pressure, basic non-volatility, easy recycling, flexible designability, safety and environmental protection, so that the ionic liquid can be applied to the field of green analytical chemistry.
The current literature reports on the application of ionic liquids in the aspect of detection and analysis of heavy metal ions only show that the environmental pollution caused in the analysis process is reduced by reducing the use of organic solvents in the process of concentrating the heavy metal ions of food samples, and all the ionic liquids adopted in environmental samples or liquid food samples, in particular hydrophobic ionic liquids such as 1-hexyl-3-methylimidazolium tetrafluoroborate and 1-hexyl-3-methylimidazolium hexafluorophosphate, are the advantages. The conventional microwave digestion method or acid digestion method is still adopted for pretreatment of the food solid sample, so that the sample is decomposed by using a strong acid strong oxidant under the conditions of high temperature and high pressure, the time and the labor are consumed, a large amount of reagents are consumed, the treatment conditions are harsh, a large amount of waste gas is generated, the health of an analyst is greatly harmed, the environment is polluted, specific equipment is required, and the sample pretreatment cost is increased. The problems of the prior pretreatment technology for detecting and analyzing the heavy metal ions in the food solid sample cannot be fundamentally solved.
The applicant finds that the hydrophilic ionic liquid has excellent dissolving performance on a food solid sample, and can quickly dissolve the sample to be analyzed under the condition of ensuring that the composition structure of the sample is not changed, so that the subsequent analysis and detection of heavy metal ions are facilitated, and a novel, simple, convenient, quick, green and safe pretreatment method is provided for the analysis and detection of the heavy metal ions with different valence states in the sample. However, the content of heavy metals in the commercially available hydrophilic ionic liquid, such as 1-butyl-3-methylimidazolium chloride ([ Bmim ] -Cl), is high through detection, and the hydrophilic ionic liquid cannot be directly used for pretreatment of food samples.
Therefore, hydrophilic ionic liquids are still to be improved, and the application of ionic liquids needs to be further developed.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the related art to some extent or to at least provide a useful commercial choice. Therefore, the invention aims to provide the hydrophilic ionic liquid with low heavy metal impurities for developing a novel, green, safe, simple and rapid pretreatment technology for detecting and analyzing heavy metal ions in a food solid sample.
The invention provides a purification method of hydrophilic ionic liquid. According to an embodiment of the invention, the method comprises: contacting sodium sulfide with a first alkaline medium, dissolving in ultrapure water, filtering, adding hydrophilic ionic liquid into the filtrate, contacting with a second alkaline medium, standing for precipitation, and filtering to obtain a liquid containing the first product.
According to the research, a sodium hydroxide rolling sweeping sulfide precipitation method is adopted for the hydrophilic ionic liquid, and the result shows that the method can be used for effectively removing heavy metal ions in the ionic liquid without interfering subsequent detection. In the step, sulfide is used to crystallize and precipitate heavy metal ions in the ionic liquid, and then the heavy metal ions are filtered to achieve the purpose of removing the heavy metal ion impurities in the ionic liquid. And the problem of overhigh cost in the purification of the conventional cation exchange membrane is well solved, or the problem that trace heavy metal impurities cannot be removed by using organic sulfides for flocculent precipitation and the subsequent detection interference is caused by introducing organic sulfides which are difficult to separate is solved.
The term "contacting" as used herein is to be understood broadly and can be any means that enables a chemical reaction of at least two reactants, such as mixing the two reactants under appropriate conditions.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The method for purifying the hydrophilic ionic liquid according to the embodiment of the invention can also have the following additional technical characteristics:
according to an embodiment of the present invention, the liquid containing the first product is further adjusted in pH with an acidic medium, the supernatant is filtered, the filtrate is concentrated and dried to near dryness, and after a small amount of liquid remaining therein is aspirated and removed, the remaining solid is frozen to obtain the first product in a crystalline state. Therefore, the adaptability of the target product is further improved, and the subsequent transportation, storage and use are facilitated.
According to the embodiment of the invention, the hydrophilic ionic liquid is an ionic liquid composed of imidazole cations, halogen element anions or acetate anions. Therefore, more and more excellent product choices can be realized.
According to the specific embodiment of the invention, the hydrophilic ionic liquid is 1, 3-dibenzylimidazole acetate, 1- (2-naphthylmethyl) -3-methylimidazole acetate, 1-heptyl-3-methylimidazole acetate, 1-ethyl-3-methylimidazole acetate, at least one of 1-acetic acid benzyl-3-methylimidazolium salt, 1- (cyclohexylmethyl) -3-methylimidazolium acetate and 1-butyl-3-methylimidazolium chloride salt, preferably at least one of 1-ethyl-3-methylimidazolium acetate, 1-acetic acid benzyl-3-methylimidazolium salt and 1-butyl-3-methylimidazolium chloride salt, and most preferably 1-butyl-3-methylimidazolium chloride salt. Therefore, the ionic liquid which has good cellulose dissolving performance, is economical and is easy to prepare can be selected as the raw material.
According to an embodiment of the invention, said first alkaline medium and said second alkaline medium are both sodium hydroxide solutions; according to a specific embodiment of the invention, the concentration of the sodium hydroxide solution is 200 g/L. Thereby, the precipitation efficiency is advantageously improved.
According to an embodiment of the invention, the ratio of the amount of sodium sulphide to the first alkaline medium is (0.4:1) g/mL. This is advantageous in improving efficiency.
According to an embodiment of the present invention, the ratio of the amount of sodium sulfide to the hydrophilic ionic liquid is (0.4:5) g/g. Therefore, materials are fully contacted, the reaction is fully carried out, and the purity of the target product is improved.
According to an embodiment of the invention, the mass ratio of said sodium sulphide to said second basic medium is (0.4:4) g/mL. This is advantageous in improving efficiency.
According to the embodiment of the invention, the filtration in the purification method of the application adopts a 0.22 μm microporous membrane. Therefore, the purpose of removing heavy metal ion impurities in the ionic liquid can be achieved.
According to an embodiment of the invention, the acidic medium is an acid corresponding to a hydrophilic ionic liquid. According to the specific embodiment of the invention, when the hydrophilic ionic liquid is 1-butyl-3-methylimidazolium chloride, the acidic medium is preferably hydrochloric acid. This makes it possible to remove excess sodium sulfide on the one hand and to form the corresponding salts on the other hand.
According to the embodiment of the invention, the pH value is 6-7, and preferably 6. This allows the formation of salts in the case of weak acids.
According to an embodiment of the present invention, the freezing condition is low temperature freezing at-4 ℃ for 2 h. The target product in a crystalline state can be formed with higher purity and is convenient for storage and transportation.
According to an embodiment of the present invention, the content of heavy metals in the hydrophilic ionic liquid is less than 0.02 μ g/g.
According to the embodiment of the invention, the hydrophilic ionic liquid is pretreated by adopting an ashing method, and three elements of Pb, Cd and Cr are detected by adopting a graphite furnace atomic absorption spectrometry. The atomic absorption spectrometry of a graphite furnace generally comprises the steps of adding about 10 mu L of a digestion solution of a pretreated sample into a graphite tube, heating the graphite tube by current, drying, ashing, atomizing and the like the sample in the graphite tube, thereby carrying out atomic absorption analysis, and determining the content of heavy metal by comparing with a standard curve. The instrument has the advantages of low detection limit, high sensitivity, simple operation and quick detection, and is suitable for analyzing the content of trace heavy metals in a sample.
According to an embodiment of the present invention, the hydrophilic ionic liquid pretreatment step comprises: (1) weighing 3g of hydrophilic ionic liquid, placing the hydrophilic ionic liquid in a quartz beaker, heating the quartz beaker at the temperature of between 200 and 250 ℃, adjusting the temperature to about 500 ℃ after the solution in the quartz beaker is dried and does not bubble any more, and heating the quartz beaker until no white smoke is emitted; (2) transferring the quartz beaker into a muffle furnace, ashing at about 700 ℃, taking out after 5 hours, and cooling to room temperature; (3) adding 0.5mL of concentrated nitric acid and 2mL of deionized water, heating at about 120 ℃ for 2-5min, taking down, cooling to room temperature, transferring the solution into a 25mL colorimetric tube, washing the quartz beaker with 1mL of deionized water for multiple times, transferring the quartz beaker into the colorimetric tube, fixing the volume to 10mL, uniformly mixing, and measuring.
The invention also provides an application of the hydrophilic ionic liquid in pretreatment of food solid sample analysis. The treated ionic liquid can be used as a solvent for pretreatment of a food solid sample.
The purification method of the hydrophilic ionic liquid according to the embodiment of the invention can realize at least one of the following advantages:
1. according to the purification method of the hydrophilic ionic liquid, which is disclosed by the embodiment of the invention, a sodium hydroxide rolling sweeping sulfide precipitation method is adopted, and the result shows that the method can be used for effectively removing heavy metal ions in the ionic liquid without interfering subsequent detection;
2. according to the purification method of the hydrophilic ionic liquid, disclosed by the embodiment of the invention, the reaction can be rapidly carried out, the operation is simple and convenient, and the reaction efficiency is greatly improved;
3. the content of heavy metal in the purified aqueous ionic liquid provided by the invention is lower than 0.02 mu g/g; provides a high-quality pretreatment solvent for food solid samples, and can further expand the application field of the sample liquid.
4. According to the purification method of the present invention, if a lower heavy metal content is required, the purification process can be repeated.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
FIG. 1 shows a calibration curve of a Pb solution according to example 4 of the present invention;
FIG. 2 shows a standard curve for a Cd solution according to example 4 of the invention;
FIG. 3 shows a calibration curve of a Cr solution according to example 4 of the present invention.
Detailed Description
The following describes embodiments of the present invention in detail. The following examples are illustrative only and are not to be construed as limiting the invention. The examples, where specific techniques or conditions are not indicated, are to be construed according to the techniques or conditions described in the literature in the art or according to the product specifications. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.
The main reagents are as follows: sodium sulfide (analytically pure), sodium hydroxide (guaranteed reagent), concentrated nitric acid (analytically pure, concentration of 68%), perchloric acid (analytically pure, concentration of 70%), multi-element mixed standard solution (GBW08607), ammonium dihydrogen phosphate (analytically pure), ammonium dihydrogen phosphate solution (concentration of 2%).
Mixing standard solutions: the mixed standard solution of Pb, Cr, Cd and other elements purchased from China institute of metrology science, wherein the concentration of Pb is 1.03 mu g/g, the concentration of Cd is 0.104 mu g/g, and the concentration of Cr is 0.516 mu g/g.
Ionic liquid (1-butyl-3-methylimidazolium chloride, [ Bmim ] -C1): CAS: 79917-90-1, obtained from commercial sources.
Main experimental apparatus and equipment: an atomic absorption spectrophotometer (AA280Z), a chromium hollow cathode lamp, a lead hollow cathode lamp, a cadmium hollow cathode lamp, a 1.5mL sample cup, and a pyrolytic graphite tube, all produced by Agilent, USA; electronic balance (mettleltolo-tomado limited), muffle FO610C (yamata japan), vacuum oven (memott trade limited).
The initial graphite furnace temperature-rising program setting conditions for detecting the Pb, Cd and Cr elements refer to the current national standard: GB5009.12-2017, GB5009.15-2014 and GB 5009.123-2014.
Pb element measurement conditions: measuring wavelength: 283.3nm, lamp current: 6.0mA, slit 0.5nm, background subtraction mode: zeeman background, the sample size was 10. mu.L, the sample size of the matrix modifier was 10. mu.L, the matrix modifier was a solution of ammonium dihydrogen phosphate (concentration: 2% by mass), the data were recorded using the peak heights, and the temperature-raising program for the graphite furnace is shown in Table 1.
TABLE 1 graphite furnace temperature-raising procedure for Pb determination
Determination conditions of Cd element: measuring wavelength: 228.8nm, lamp current: 7.0mA, slit 0.2nm, background subtraction mode: zeeman background, sample size 10. mu.L, matrix modifier 10. mu.L, and ammonium dihydrogen phosphate solution (concentration 2 mass%), and the peak height data were recorded, and the temperature program of the graphite furnace is shown in Table 2.
TABLE 2 graphite furnace temperature program for Cd determination
Cr element measurement conditions: measuring wavelength: 357.9nm, lamp current: 7.0mA, slit 0.2nm, background subtraction mode: zeeman background, sample size 10. mu.L, matrix modifier 10. mu.L, and ammonium dihydrogen phosphate solution (concentration 2 mass%) as matrix modifier, and the peak height data are recorded, and the temperature program of graphite furnace is shown in Table 3.
TABLE 3 graphite furnace temperature program for Cr determination
EXAMPLE 1 preparation of solutions
Preparation of NaOH solution (200 g/L): 100g of sodium hydroxide is weighed, slowly added into a proper amount of ultrapure water for dissolving, continuously stirred, and added with ultrapure water to reach the constant volume of 500 mL.
Preparing a sodium sulfide solution: 4g of sodium sulfide crystals were weighed, 10mL of NaOH solution (200g/L) and 50mL of ultrapure water were added, and after dissolving, filtration was carried out using a 0.22 μm microporous membrane.
Mixing standard stock solutions: 2mL of the multi-element mixed standard solution (GBW 08607: wherein the Pb concentration is 1.03. mu.g/g, the Cd concentration is 0.104. mu.g/g, and the Cr concentration is 0.516. mu.g/g) was removed. Dissolving in 25mL deionized water, shaking and shaking to obtain a mixed standard stock solution with Pb concentration of 82.4 mug/L, Cd concentration of 8.32 mug/L and Cr concentration of 41.28 mug/L.
Example 2 preparation of hydrophilic Ionic liquids
Commercially available [ BMIM ] -Cl (3g) was weighed and added to the sodium sulfide solution (50mL) of example 1, after complete dissolution, 4mL of NaOH solution was added, the mixture was allowed to stand for 10min to completely precipitate, and then filtered through a 0.22 μm microporous membrane, and distilled under reduced pressure to obtain purified 1-butyl-3-methylimidazole chloride.
Example 3 preparation of hydrophilic Ionic liquids in crystalline form
Sodium sulfide crystals (0.4g) were weighed, and 200g/L NaOH solution (1mL) and ultrapure water (5mL) were added thereto, and after dissolving, they were filtered through a 0.22 μm microporous membrane. Weighing commercially available ionic liquid [ BMIM ] -Cl (0.3g), adding NaOH solution (0.4mL) after completely dissolving, standing for 10min to completely precipitate, filtering with a 0.22 mu m microporous filter membrane, adding concentrated hydrochloric acid until the pH value of the solution is 6, wherein precipitates can appear at this time, taking supernatant after naturally settling, filtering with the 0.22 mu m microporous filter membrane again, heating the filtrate at 100-140 ℃ to a small volume, transferring to a vacuum oven, drying at 80 ℃ and 20mbar to near dryness, sucking out and removing the residual small amount of liquid, freezing the residual solid in a molten semi-fluid state at-4 ℃ for 2 hours to obtain a blocky product, and crushing the blocky product to obtain the crystalline 1-butyl-3-methylimidazole chloride.
Example 4 Standard Curve was prepared
Transferring a proper amount of mixed standard stock solution (GBW 08607: wherein the Pb concentration is 1.03 mug/g, the Cd concentration is 0.104 mug/g and the Cr concentration is 0.516 mug/g) into a volumetric flask, and fixing the volume to the scale to prepare a series of mixed standard solutions. The series of mixed standard solutions were used, initial graphite furnace temperature program conditions were set with reference to the current national standards, and instrumental automatic standard curve measurements were performed, and the results obtained are shown in tables 4, 5, and 6.
TABLE 4 Absorbance of Pb Standard solutions of different concentrations
TABLE 5 Absorbance of Cd Standard solutions of different concentrations
TABLE 6 absorbance of Cr standard solutions of different concentrations
The standard curves of Pb, Cd and Cr are plotted in tables 4-6 and shown in FIG. 1, FIG. 2 and FIG. 3. Therefore, the following steps are carried out: the standard curve for Pb solution is abs (Pb) 0.0087 xc (μ g/L) +0.0147, with a correlation of 0.997; the standard curve for Cd solution is abs (Cd) ═ 0.0292 xc (μ g/L) +0.0087, with a correlation of 0.999; the standard curve of the Cr solution is abs (Cr) 0.0035 × C (μ g/L) +0.0452, and the correlation is 0.999. The standard curves and the correlation degree thereof can prove that the instrument has good linear correlation and high sensitivity when detecting the Pb, Cd and Cr heavy metal elements.
Example 5 determination of heavy Metal content in aqueous Ionic liquids before and after purification
The method comprises the following steps of pretreating the hydrophilic ionic liquid by adopting a dry ashing method before detection: (1) weighing 3g of hydrophilic ionic liquid, placing the hydrophilic ionic liquid in a quartz beaker, heating the quartz beaker at the temperature of between 200 and 250 ℃, adjusting the temperature to about 500 ℃ after the solution in the quartz beaker is dried and does not bubble any more, and heating the quartz beaker until no white smoke is emitted; (2) transferring the quartz beaker into a muffle furnace, ashing at about 700 ℃, taking out after 5 hours, and cooling to room temperature; (3) adding 0.5mL of concentrated nitric acid and 2mL of deionized water, heating at about 120 ℃ for 2-5min, taking down, cooling to room temperature, transferring the solution into a 25mL colorimetric tube, washing the quartz beaker with 1mL of deionized water for multiple times, transferring the quartz beaker into the colorimetric tube, fixing the volume to 10mL, uniformly mixing, and measuring.
The heavy metal content in a batch of [ Bmim ] -Cl directly purchased from the market and the heavy metal content in the ionic liquid obtained by purifying the batch of [ Bmim ] -Cl in example 2 were respectively detected by graphite furnace atomic absorption spectrometry, and two parallel samples were simultaneously prepared. The comparative results are shown in Table 7.
TABLE 7 heavy metal content before and after purification in commercially available [ Bmim ] -Cl
(1# is an ionic liquid sample, 2# and 3# are ionic liquids after purification treatment; ND represents below the detection limit of the apparatus)
The result shows that the heavy metal ion impurities contained in the [ Bmim ] -Cl treated by the sodium hydroxide rolling sulfide precipitation method are trace heavy metal impurities, the content is extremely low, and the treated [ Bmim ] -Cl can reach the purity required by the subsequent detection. From this, it is known that the treatment of the ionic liquid [ Bmim ] -Cl with sodium hydroxide rolling sulfide precipitation method can reduce the heavy metal ion impurities therein to a desired concentration.
Comparative example 1 determination of heavy metal content in aqueous ionic liquid after purification by conventional precipitation method
Commercially available [ Bmim ] -Cl (3g) was weighed, sodium sulfide (4g) and ultrapure water (50mL) were added, and the mixture was stirred until the crystals were completely dissolved and filtered using a 0.22 μm microporous membrane. The filtrate was heated with an electric hot plate, and the sample was treated by dry ashing as described in example 5, to obtain the final digest with a constant volume of 50mL, and two parallel samples and blanks were prepared. And finally, detecting by using graphite furnace atomic absorption spectrometry. The results are shown in Table 8.
TABLE 8 concentration of Pb in the solution after treatment by conventional precipitation
Since for trace heavy metal ions it was already possible to precipitate it completely by adding 4g of sodium sulphide, it can be seen from table 8: although the sulfide precipitation method can achieve a good effect of removing heavy metal impurities, for the experiment, if the solvent contains Pb impurities with the concentration of 1-2 mug/g, the Pb concentration after constant volume is 0.5-2 mug/L because the solvent required by the experiment is 3-5 g and the constant volume is 50mL, the subsequent detection experiment is greatly interfered, and the same is true for Cd and Cr elements.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (13)
1. A method for purifying hydrophilic ionic liquid is characterized in that,
contacting sodium sulfide with a first alkaline medium, dissolving in ultrapure water, filtering, adding hydrophilic ionic liquid into the filtrate, contacting with a second alkaline medium, standing for precipitation, and filtering to obtain a liquid containing a first product;
further adjusting the pH value of the liquid containing the first product by using an acidic medium, taking supernatant liquid, filtering, concentrating filtrate, drying to be nearly dry, sucking out and removing a small amount of liquid remained in the filtrate, and freezing the remained solid so as to obtain the first product in a crystalline state;
the hydrophilic ionic liquid is 1-butyl-3-methylimidazole chloride salt;
the pH value is 6.
2. The purification process according to claim 1, wherein the first basic medium and the second basic medium are both sodium hydroxide solutions.
3. The purification process according to claim 2, wherein the concentration of the sodium hydroxide solution is 200 g/L.
4. The purification process according to claim 1, wherein the ratio of the amount of sodium sulfide to the first basic medium is (0.4:1) g/mL.
5. The purification process according to claim 1, wherein the amount ratio of sodium sulfide to hydrophilic ionic liquid is (0.4:5) g/g.
6. The purification process according to claim 1, characterized in that the mass ratio of the sodium sulfide to the second basic medium is (0.4:4) g/mL.
7. The purification method according to claim 1, wherein the filtration is performed by using a 0.22 μm microporous membrane.
8. The purification process according to claim 1, characterized in that the acidic medium is hydrochloric acid.
9. The purification method according to claim 1, wherein the freezing condition is low temperature freezing at-4 ℃ for 2 h.
10. The purification process according to claim 1, wherein the hydrophilic ionic liquid has a heavy metal content of less than 0.02 μ g/g.
11. The method for detecting the hydrophilic ionic liquid purified by the purification method according to claim 1, wherein the hydrophilic ionic liquid is pretreated by an ashing method, and three elements of Pb, Cd and Cr are detected by graphite furnace atomic absorption spectrometry.
12. The method of claim 11, wherein the preprocessing step comprises:
(1) weighing 3g of hydrophilic ionic liquid, placing the hydrophilic ionic liquid in a quartz beaker, heating at 200-250 ℃, adjusting the temperature to about 500 ℃ after the solution in the quartz beaker is dried and does not bubble any more, and heating until no white smoke is emitted;
(2) transferring the quartz beaker into a muffle furnace, ashing at about 700 ℃, taking out after 5 hours, and cooling to room temperature;
(3) adding 0.5mL of concentrated nitric acid and 2mL of deionized water, heating at about 120 ℃ for 2-5min, taking down, cooling to room temperature, transferring the solution into a 25mL colorimetric tube, washing the quartz beaker with 1mL of deionized water for multiple times, transferring the quartz beaker into the colorimetric tube, fixing the volume to 10mL, uniformly mixing, and measuring.
13. Use of the hydrophilic ionic liquid purified by the purification method according to claim 1 in the pretreatment of food solid sample analysis.
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| CN114414509B (en) * | 2021-12-30 | 2023-12-12 | 通标标准技术服务（天津）有限公司 | Method for detecting heavy metal chromium in food |
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